Refrigeration and Air-conditioning Unit-4.pptx

Introduction to Air conditioning.
Standards of temperature, humidity and air motion.
Components of air conditioning system.
Summer air conditioners.
Winter air conditioners.
Year – round air conditioners.
Window air conditioners.

Split air conditioners.
Central air conditioning systems.
Air distribution system.
Thermal insulation of air conditioning systems.
Applications of air conditioning system.

1. Unit - 4 Air conditioning system

2. A air conditioning system is defined as an assembly of different parts of the system used to produce a specified condition of air within a space of building. Standards of temperature: Standard temperature and pressure (STP) refers to the nominal conditions in the atmosphere at sea level(o C&1bar) Normal Temperature and Pressure, which is defined as a temperature of 20 °C and a pressure of 1 atm. It is advisable to maintain the AC temperature at 24-25 degrees Celsius as it is considered most optimum for healthy bodily functions. Components in air conditioning system: Fan Supply ducts Supply outlets Space to be conditioned Return outlets Return ducts Filter Heating chamber or cooling coil.

3. Fan : The primary function of a fan is to move air to and from the room. Out door air, indoor air and combination of indoor and outdoor air. The fan pulls air from outdoors or from the room but in most systems it pulls air from both sources the same time. The amount of air supplied by the fan must be regulated since drafts in the room cause discomfort, and poor air movement slows the heat rejection processes. Supply duct : The function of a supply duct is to direct the air from fan to the room. In order that air may flow freely it should be as short as possible and have minimum number of turns. Supply outlets : The function of supply outlets is to distribute the air evenly in a room. supply outlets can either fan or jet the air stream, This direction control plus the location and the number of outlets in the room contribute a great deal to comfort or discomfort effect of air pattern.

4. Space : It is very important to have an enclosed space since if it does not exist it would be impossible to complete the air cycle since conditioned air from supply outlets would flow into the atmosphere. Return outlets: These are the openings in the room surface. They are employed to allow room air to enter the return duct They are usually located at opposite extreme of a wall or room from the supply outlet Filters : A filter is primarily used to clean the air by removing dust and dirt particles. They are usually located at some point in the return air duct. They are made of any materials from spun glass to composite plastic. Other types operate on electrostatic principle. Cooling coil and heating coil : The cooling coil and heating coil or combustion chamber can be located either ahead or after the fan, but should always be located after the filter. A filter ahead of the coil is necessary to prevent the excessive dirt, dust and dirt particles from covering the coil surface. Summer operation: The air-conditioning cycle cools the air during summer operation. Return air from the room passes over the surface of cooling coil, and the air cooled to the required temperature. If there is too much moisture present, it is removed automatically as the air is cooled by the coil. Winter operation: The air-conditioning cycle adds heat to the air during winter operation. This is achieved by passing the return air from the room over the surface of a heating coil.

5. CLASSIFICATION OF AIR-CONDITIONING SYSTEMS According to the arrangement of equipment Central systems Unitary systems Unitary-central systems 2. According to the purpose Comfort air-conditioning system Industrial air-conditioning system 3. According to season of the year Winter air-conditioning system Summer air-conditioning system Year-round air-conditioning system Zoned systems

6. Summer Air Conditioning System It is the most important type of air conditioning, in which the air is cooled and generally dehumidified. The outside air flows through the damper, and mixes up with recirculated air (which is obtained from the conditioned space). The mixed air passes through a filter to remove dirt, dust and other impurities. The air now passes through a cooling coil. The coil has a temperature much below the required dry bulb temperature of the air in the conditioned space. The cooled air passes through a perforated membrane and loses its moisture in the condensed form which is collected in a sump. After that, the air is made to pass through a heating coil which heats up the air slightly. This is done to bring the air to the designed dry bulb temperature and relative humidity.

7. Now the conditioned air is supplied to the conditioned space by a fan. From the conditioned space, a part of the used air is exhausted to the atmosphere by the exhaust fans or ventilators. The remaining part of the used air (known as recirculated air) is again conditioned. The outside air is sucked and made to mix with the recirculated air in order to make up for the loss of conditioned (or used) air through exhaust fans or ventilation from the conditioned space. Components in Summer Air Conditioning System: Damper Filter Cooling coil Heating coil Sump Fan

8. Winter Air Conditioning Systems In winter the outside conditions are cold and dry. As a result, there will be a continuous transfer of sensible heat as well as moisture (latent heat) from the buildings to the outside. In winter air conditioning, the air is heated, which is generally accompanied by humidification. The outside air flows through a recirculated air (which is obtained from the conditioned space). The mixed air passes through a filter to remove dirt, dust and other impurities. The air now passes through a preheat coil in order to prevent the possible freezing of water and to control the evaporation of water in the humidifier. After that, the air is made to pass through a reheat coil to bring the air to the designed dry bulb temperature. Now, the conditioned air is supplied to the conditioned space by a fan. from the conditioned space, a part of the used air is exhausted to the atmosphere by the exhaust fans or ventilators. The remaining part of the used air (known as recirculated air) is again conditioned.

9. The outside air is sucked and made to mix with recirculated air, in order to make up for the loss of conditioned (or used) air through exhaust fans or ventilation from the conditioned space. Components in Winter Air Conditioning System: Damper Filter Pre heater Humidifier Reheat coil Fan

10. Year-Round Air Conditioning System The year-round air conditioning system should have equipment for both the summer and winter air conditioning. The outside air flows through the damper and mixes up with the recirculated air (which is obtained from the conditioned space). The mixed air passes through a filter to remove dirt, dust and other impurities. In summer air conditioning, the cooling coil operates to cool the air to the desired. Year-round air conditioning system. value. The dehumidification is obtained by operating the cooling coil at a temperature lower than the dew point temperature (apparatus dew point). In winter, the cooling coil is made inoperative and the heating coil operates to heat the air. The spray type humidifier is also made use of in the dry season to humidify the air.

11. Components in Year-Round Air Conditioning System: Damper Filter Cooling coil Humidifier Heating coil Fan

12. Window type package units A package unit is a self-contained unit because the complete unit including evaporator and condensing unit is all incorporated in a common enclosure The normal capacity of such a unit is 1 and 1.5 tones These are window mounting models which are normally capable of cooling, heating, cleaning and circulating the air. The air distribution is met by a grill arrangement which also allows fresh air through dampers. The dampers are also provided for exhaust purposes. Components in Window type Air Conditioning System: Compressor Condenser Evaporator Capillary tube Fan Filter Blower

13. Split type air conditioner Split air conditioners are used for rooms and halls, usually in places where window air conditioners cannot be installed. The split type room air conditioner is comprised of two parts. The outdoor unit The indoor unit The outdoor unit This unit houses important components of the air conditioner like the compressor, condenser coil and also the expansion coil or capillary tubing. This unit is installed outside the room or office space which is to be cooled.   Compressor  is the main component of the system and is used to compress the refrigerant. Condenser Coil  is used to reject heat from the refrigerant to the out side air. Condenser Fan  is used in air-cooled condenser to help move the air molecules over the surface of the condensing coil, hence rejecting the heat form the indoor to the space outside the building.

14. INDOOR UNIT : The indoor unit houses the evaporator coil or the cooling coil, a long blower and the Freon fluid enters the cooling coil. The blower sucks the hot, humid and filtered filer. After passing from the expansion coil, the chilled air from the room and it blows over the cooling coil.  Evaporator coil  is where the heat exchange is done with the room. It consists of fins and tubes. Control Panel  is where user control the functions of the air conditioner. Displays at the panel may indicate the mode of operation, timer, on/off status, fan speed and other special functions. Air Filter  is located in front of the evaporator coil to trap any dust or particles before going into the evaporator. This is usually washable and re-useable. Users are advised to clean it at least once in three months or more regularly if the environment is dirty. Supply and Return Air Grills  are where the air enters and discharge from the indoor unit.

15. Fan blower  together with its motor are used to control the fan speed of the unit. High, medium. Low and Ultra low speeds are usually designed for users to select. Capillary tube  is used as an expansion device where the flow of the refrigerant depends on the tube internal diameter, shape and its length. The tube is usually used in smaller units. WORKING A copper connection pipe and electrical wiring connects the indoor unit to the outdoor unit of the split air conditioning. Gas refrigerant is pumped from the outdoor condenser coil and compressor through the connection pipe to the indoor unit(s). A fan then quietly distributes cool air drawn across the unit’s evaporator coil.

16. Central air conditioning systems This type of system is suitable for air-conditioning large space such as theatres, cinemas, restaurants, exhibition halls, or big factory spaces where no sub-division exists. The central systems are generally employed for the loads above 25 tones of refrigeration and 2500 m³/min of conditioning air. The unitary systems can be more economically employed for low capacity (below 25 tones) units. In central system, the equipment such as fans, coils, filters and their encasement are designed for assembly in the field. A central system serves differing rooms, requires individual control of each room. The condenser. compressor, dampers, heating, cooling and humidifying coils and fan are located at one place say basement. The conditioned air is carried to the different rooms by means of supply ducts and returned back to the control plant through return ducts. Part of the supply air to the rooms may be exhausted outdoors. Outdoor air enters from an intake which should be situated on that side of the building least exposed to solar heat. he air after passing through damper passes through filters. The filters may be of a mechanical cleaned type, replaceable-cell type or may be electrostatic. The cleaned air then passes to the conditioning equipment in the following order: Temperature (or pre heater) coil, cooling coil, humidifier (air washer), heating coils and finally fan.

17. Advantages of Central System: 1.Low investment cost as compared to total cost of separate unit. 2. Space occupied is unimportant as compared to a room unit conditioner which must be placed in the room. 3. Better accessibility for maintenance. 4. The running cost is less per unit of refrigeration. 5. Noise and vibration troubles are less to the people in air-conditioned places as the air- conditioning plant is far away from the air-conditioned places. 6. The exhaust air can be returned and partly reused with obvious saving in heating and refrigeration.

18. Components in central Air Conditioning System: Damper Weather hood Intake Mixing damper Volume damper Cooling coil Heating coil Spray Tempering coil Filter Access doors

19. AIR-DISTRIBUTION SYSTEMS Intake - An opening through which air is returned or exhausted from the space. Outlet - An opening through which air is supplied to the treated space. Grille - A functional or decorative covering for an outlet or in take. Resister- A grille provided with a damper. Diffuser . An outlet grille (or appurtenance) designed to guide the direction of the air. Throw- The horizontal or vertical axial distance that an air stream travels on leaving the outlet. Drop- The vertical distance the lower edge of the air stream drops between the time it leaves the outlet and the time it reaches the end of its throw. Primary air- The air coming out of the outlet. Secondary air- The room air picked up by the primary air by entrainment. Total air. The mixture of primary and secondary air. Aspect ratio- Grille-dimension ratio, length to width.

20. Types of Air-distribution Systems 1.Ejector system. 2. Downward system. 3. Upward system . Ejector system. In an "ejector system" the inlet grille ejects the air into the room and inducts sufficient velocity for circulation. Former is cheaper and very simple in construction. Letter system is known as "pan-type" arrangement. It provides more uniform distribution of air. 2. Downward system In downward system of air flow air is introduced through openings located in the ceiling and removed through the openings made in floor or in walls near the floor. 3. Upward system. In an "upward system" of flow the air outlets are located in walls near the ceiling or in the ceiling.

21. Thermal insulation Any material that retards or offers resistance to the flow of heat through it is known as 'Thermal insulator'. Thermal insulation however cannot stop the heat flow completely, but it can only retard or reduce the rate of heat flow through it. Insulating materials have extremely low thermal conductivities. Desirable properties of a good heat insulating materials are: Thermal stability Chemical stability Physical stability Low thermal conductivity Resistance to moisture Low specific heat Low specific gravity Resistance to. vibration and shock Non-inflammability Porous and fibrous texture Odourless Economical in its initial cost.

22. Classification Of Thermal Insulating Materials 1.Organic heat insulators : Cork Rubber foam Rice husk Polystyrene Cotton wool Sawdust Cork 2.Inorganic heat insulators: Glass wool Slag wool Asbestos Ceramic products

23. Applications of air conditioning system Food processing preservation and distribution Chemical and process industries Special Applications such as cold treatment of metals, medical, construction, ice skating etc. Comfort air-conditioning Industrial, such as in textiles, printing, manufacturing, photographic, computer rooms, power plants, vehicular etc. Comfort – commercial and residential